1. Field of the Invention
The present invention relates to a method for a developing processing of a substrate such as a semiconductor wafer subjected to an exposure treatment and an apparatus for supplying a developing solution.
2. Description of the Related Art
In a manufacturing process of a semiconductor device, a prescribed circuit pattern is formed on the surface of a semiconductor wafer by using a so-called “photolithography technology”. In the photolithography step, a series of treatments are carried out such that a resist film is formed on a cleaned semiconductor wafer by supplying a photoresist solution onto the semiconductor wafer, followed by exposing the resist film to light in a prescribed pattern and subsequently developing the pattern.
In the developing step, an exposed semiconductor wafer is held first by a rotatable spin chuck. Then, a puddle of a developing solution is formed by supplying a developing solution onto the surface of a semiconductor wafer held stationary by the spin chuck, and the developing solution supplied onto the surface of the semiconductor wafer is left to stand for a prescribed time so as to permit the developing reaction to proceed. In the next step, a rinsing liquid such as a pure water is supplied onto the semiconductor wafer while rotating the semiconductor wafer so as to rinse the semiconductor wafer. Finally, the supply of the rinsing liquid onto the semiconductor wafer is stopped, and the semiconductor wafer is rotated at a high speed so as to dry the semiconductor wafer by a spin drying. In this case, a TMAH solution having a fixed concentration of, for example, 2.38% by weight for the various resist materials is used as the developing solution.
Strictly speaking, however, the appropriate concentration of the developing solution differs for each resist material. Further, the appropriate concentration of the developing solution is changed with the reaction time during the developing reaction. It was possible in the past to obtain the required accuracy in, for example, the shape of the circuit pattern even if a developing solution having a predetermined concentration is used for a plurality of different resist materials. In recent years, however, a resist material having a high reactivity to the developing solution has come to be used. Further, the resist film has come to be formed thinner. Further, the light having a shorter wavelength has come to be used for the exposure, and the pattern exposed to light has been made finer and finer. Under the circumstances, it is difficult nowadays to form a satisfactory circuit pattern by the conventional method for the developing processing using a developing solution of a predetermined concentration.
Further, in the conventional method for the developing processing, which is carried out with the semiconductor wafer held stationary, a dissolved product formed by the developing reaction, which dissolves the resist film, remains in a high concentration in a part on the surface of the semiconductor wafer. Therefore, in the latter stage of the developing processing, the state of equilibrium between the dissolved product remaining in a high concentration and the developing solution is collapsed, with the result that the dissolved product is diffused toward the developing solution. It is possible for the movement of the developing solution accompanying the diffusion of the dissolved product to bring about a change in a partial critical dimension (CD), i.e., the line width of the pattern, on the wafer surface. Further, if the developing solution and the dissolved product are removed by rotating the wafer simultaneously with start-up of the supply of a rinsing liquid after the developing processing, the dissolved product leaves their traces on the wafer surface when the dissolved product of a high concentration is centrifugally expanded. Naturally, the traces of the dissolved product left on the wafer surface degrades the wafer.
As described above, the dissolved product of the resist affects the CD in the latter stage of the developing processing. What should be noted is that, since the generating amount of the dissolved product differs depending on the aperture rate of the mask, the CD distribution on the wafer surface is rendered different depending on the aperture rate of the mask in spite of the same pattern. Further, the CD in the central portion is rendered different from that in the outer circumferential portion within a single shot. In conclusion, in the conventional method for the developing processing, the CD uniformity on the substrate is not necessarily satisfactory. It was customary in the past to deal with the problem by, for example, correcting the pattern of the mask under the prescribed conditions for the developing processing. However, it is highly laborious to determine appropriately the conditions for the developing processing.
What should also be noted is that, if a pure water is supplied onto a semiconductor wafer after completion of the developing reaction, the pH value of the developing solution on the semiconductor wafer is rapidly lowered, with the result that the dissolved product is precipitated in the form of a solid material so as to be attached to the developing pattern, thereby generating a defect.